Oceanological aspects of acoustic monitoring of Arctic Ocean climate

The Arctic Ocean is an important object of investigation in the global ATOC program because of its crucial role in the heat balance of the Northern Hemisphere. Although the temporal and spatial variability of the sound speed in the Arctic Ocean is relatively weak, the Arctic ice cover essentially complicates modeling of the acoustic response to climate change. Moreover, the influence of the strongly varying ice cover causes additional difficulties in interpretation of the results of acoustic ocean thermometry for several reasons: (1) the extremely strong influence of ice distribution on the ocean–atmosphere heat exchange, (2) the long-term variation of the ice cover, and (3) the specific response of the surface water sound speed to heating of an ice-covered sea (a heat input should decrease the sound speed under melting ice). Under-ice winter convection can also create specific kinds of inhomogeneities of the Arctic Ocean (chimneys, plumes of dense water, etc.). Additional serious difficulties arise because of strong dependency of Arctic climate on the heat inflow of both the Atlantic and Pacific Oceans. This changeable inflow can cause long-term variations of the Arctic Ocean. It seems worthwhile to begin the Arctic ATOC with the installation of acoustic tracks across the Fram Strait.